Because our authentication system reads cookies from the initial
connection attempt, several SockJS transports can't be used.
(imported from commit 34b9571225d39072985b8223fb12c43c7235841f)
New dependency: sockjs-tornado
One known limitation is that we don't clean up sessions for
non-websockets transports. This is a bug in Tornado so I'm going to
look at upgrading us to the latest version:
https://github.com/mrjoes/sockjs-tornado/issues/47
(imported from commit 31cdb7596dd5ee094ab006c31757db17dca8899b)